1. Field of the Invention
The present invention relates to a process for producing an aromatic polyimide powder molded body which maintains an extremely high level of heat resistance while also having particularly high mechanical characteristics such as elongation, strength, etc., and which contains, for example, a 3,3',4,4'-biphenyltetracarboxylic acid component as major units, a 2,3,3',4'-biphenyltetracarboxylic acid component as minor units and para-phenylenediamine as an aromatic diamine component, as well as to an aromatic polyimide powder which is used for the production process.
2. Description of the Related Art
Conventional processes for producing polyimide powder molded bodies comprising 3,3',4,4'-biphenyltetracarboxylic acid components and para-phenylenediamine components are described, for example, in Japanese Unexamined Patent Publication No. 61-241326 and Japanese Unexamined Patent Publication No. 1-266314.
These documents present molded bodies with excellent mechanical characteristics such as heat resistance, dimensional stability and compressive strength.
However, the polyimide powders described in these publicly known documents have essentially unmeasured melting points (or glass transition points), and because of inadequate fusion between the powder during hot compression molding, some of the mechanical characteristics, particularly flexural strength and tensile strength, have not always been satisfactory.
Other indicated problems include low productivity by loss during molding, because the elongation, flexural strength and tensile strength have been insufficient during secondary working of the molded bodies into various shapes by cutting, etc.
Consequently, attempts have been made to improve the fusibility between the powder during hot compression molding, in order to increase the elongation and the mechanical characteristics of such molded bodies.
For example, one attempted process has been compression molding polyimide powder obtained by mixing a thermoplastic polyimide with a polyimide comprising a 3,3',4,4'-biphenyltetracarboxylic acid component and a para-phenylenediamine component, but this has also been associated with certain drawbacks, since uniform mixture of the two components with totally different properties is difficult, and the mechanical strength and elongation of the resulting molded bodies have still not reached satisfactory levels, while the heat resistance is in fact lower.
Consequently, according to the prior art it has not been possible to obtain aromatic polyimide powder molded bodies with satisfactory heat resistance, mechanical strength and elongation.